Efficiency Enhancement Of Concurrent Dual-band Power Amplifiers

In recent years, along with the fast evolution of3G/4G communicationsystems, concurrent dual-band power amplifiers (PAs), which can deal with twoseparated frequency bands simultaneously, has received wide concerns. Usingconcurrent dual-band PAs, the flexibility of communication systems can beimproved, the construction cost of wireless infrastructure can be reduced, andthe implementation of carrier aggregation can be made easier. However, up totoday, dual-band PAs has not been used in industrial applications. The mainreason lays on the fact that most previously reported concurrent dual-band PAssuffer from evident performance degradation in concurrent mode.In this paper, efforts will be made to solve the problem of performancedegradation. At first, a novel method, which can be referred as concurrentcontinuous wave (CW) analysis, is introduced to perform theoretical analysis ofconcurrent dual-band PAs. According to the analysis, the drain current ofdual-band PAs contains significant intermodulation (IM) components, whichmust be matched properly, and in this way, the concept of IM tuning isintroduced. It will be proven that the absence of IM tuning is the main cause toperformance degradation in previously reported dual-band PAs.Additionally, in this paper the concept of reachable region is introduced todescribe the output capacity of concurrent dual-band PAs. And it is shown thatthe mismatch between the modulated signals’ two dimensional (2D) distributionand the reachable region of PA is another reason of performance degradation.To solve such a problem, a2D crest factor reduction method is introduced,whose main idea is reshaping the2D distribution to match the PA’s reachableregion.To verify the feasibility of IM tuning, several design examples are given inthis paper. One of the example PAs is a1.9/2.6GHz concurrent dual-bandDoherty PA (DPA), which is designed using two13Watts GaN HEMTs. TheDPA is measured in concurrent using modulated signals. In the measurement,two10MHz LTE signals which are processed in advance using a2D CFR procedure are utilized as the stimulus, at the1.9and2.6GHz bands respectively.According to the measured results, after linearization, the fabricated DPAexhibits a power added efficiency (PAE) higher than45.8%and output powerclosed to10Watts. The performance is compared with state-of-the-artperformances, and according to the comparison, the measured performanceexhibits an evident improvement in both efficiency and output power.